Secondary battery with autolytic dendrites

ABSTRACT

A battery ( 100 ) comprises a cell having a cathode compartment ( 120 ) that includes an element that is oxidized during charging of the battery ( 100 ), wherein the oxidized element forms a salt with an acid and thereby increases the H+ concentration in the cathode compartment ( 120 ) sufficient to promote an H+ flux into the anode compartment ( 110 ) across the separator ( 130 ), wherein the H+ flux across the separator ( 130 ) is sufficient to disintegrate a zinc dendrite proximal to the separator ( 130 ).

FIELD OF THE INVENTION

The field of the invention is batteries, and especially secondarybatteries in which zinc forms a redox couple with a second element.

BACKGROUND OF THE INVENTION

Many types of secondary batteries and other power cells are known, basedupon a relatively wide range of electrical couples, and among the mostpopular electrical couples are those containing zinc.

For example, zinc may form a redox pair with nickel to provide arechargeable redox system. While many rechargeable zinc/nickel batteriesfrequently exhibit a relatively good power to weight ratio, severalproblems of the zinc/nickel redox pair persist. Among otherdifficulties, such batteries tend to have a comparably poor cycle lifeof the zinc electrode. Moreover, nickel is known to be a carcinogen inwater-soluble form, and is thus problematic in production and disposal.

To circumvent at least some of the problems with toxicity, zinc maybecombined with silver oxide to form a secondary battery. Rechargeablezinc/silver batteries often have a relatively high energy and powerdensity. Moreover, such batteries typically operate efficiently atextremely high discharge rates and generally have a relatively long dryshelf life. However, the comparably high cost of the silver electrodegenerally limits the use of zinc/silver batteries to applications wherehigh energy density is a prime requisite.

In a further, relatively common secondary battery, zinc is replaced bycadmium and forms a redox couple with nickel. Such nickel/cadmiumbatteries are typically inexpensive to manufacture, exhibit a relativelygood power to weight ratio, and require no further maintenance otherthan recharging. However, cadmium is a known toxic element, and therebyfurther increases the problems associated with health and environmentalhazards. Thus, despite the relatively widespread use of secondarybatteries numerous problems, and especially problems associated withtoxicity and/or relatively high cost persist.

Still further, all or almost all of the known secondary batteries needto be operated over several charge/discharge cycles under conditions inwhich the cathode compartment is separated from the anode compartment bya separator. Loss of the separation will typically result in undesiredplating of one or more components of the electrolyte on the batteryelectrode and thereby dramatically decrease the performance of suchbatteries.

Unfortunately, zinc contained in most zinc containing electrolytes hasthe tendency to form zinc dendrites during charging, wherein dendritegrowth typically proceeds towards the separator and frequently resultsin contact, if not even damage to the separator. Thus, prevention ofzinc dendrite growth has received considerable attention over the recentyears, and various approaches have been made to reduce the riskassociated with dendrite growth.

In one approach, electrolyte additives are used to prevent dendriteformation. For example, in U.S. Pat. No. 3,793,079 the inventorsdescribe addition of various organic compounds having an oxygen etherand a sulfonamide group to reduce dendrite formation. Alternatively, asdescribed in U.S. Pat. No. 3,811,946 the reaction product of an amineand an aldehyde are employed as organic additives to reduce dendriteformation. Further known compositions for reduction of dendrites includebenzotriazole, benzene sulfonamide, toluene sulfonamide, chlorotoluenesulfonamide and thiourea. However, while at least some of the knowncompounds work relatively well for their intended purpose, newdifficulties arise. Among other things, at least some of the knowncompounds exhibit oxidation and/or decomposition by oxidizing agents inmost rechargeable batteries. Furthermore, such compounds may interferewith reversibility of either electrode. Moreover, it has been found thatsome additives tend to precipitate or salt out during repeatedrecharging.

In another approach, surfactants may be employed to reduce dendriteformation as described, for example, in U.S. Pat. No. 4,074,028 and4,040,916. Here, formation of a non-dendritic zinc layer is achieved byincluding 0.001 to 10 weight percent of a non-ionic surfactant additive(oxaalkyl or polyoxaalkyl perfluoroalkane sulfonamide) in thezinc-containing electrolyte. While surfactants may work satisfactorilyfor various electroplating and battery applications over a relativelyshort period, electrochemical (and other) degradation will eventuallylimit the usefulness of such compounds, especially in acid electrolytes.

Although numerous secondary batteries are known in the art, all oralmost all of them suffer from one or more disadvantages. Particularly,the performance of known secondary batteries will significantly decreasewhen anolyte and catholyte of such batteries will inadvertently mix dueto dendrite growth that damages the separator. Therefore, there is stilla need to provide improved batteries.

SUMMARY OF THE INVENTION

The present invention is directed to a battery comprising a cathode andan anode compartment and a zinc-containing electrolyte, wherein thebattery is configured such that zinc dendrites growing from the anodewill disintegrate proximal to the separator that separates the cathodeand the anode compartment.

Especially contemplated batteries include a cell with an acidelectrolyte, wherein the cell is at least partially divided by a H⁺permeable separator into an anode compartment and a cathode compartment,wherein the acid electrolyte in the anode compartment comprises zinc,and wherein the acid electrolyte in the cathode compartment comprises anelement that is oxidized during charging of the battery, wherein theoxidized element forms a salt with an acid, thereby increasing an H⁺concentration in the cathode compartment sufficient to promote an HIflux into the anode compartment across the separator, and wherein the H⁺flux across the separator is sufficient to disintegrate a zinc dendriteproximal to the separator.

In one aspect of the inventive subject matter, contemplated acidelectrolytes comprise an organic acid or inorganic acid (e.g., methanesulfonic acid, trifluoromethane sulfonic acid, perchloric acid, nitricacid, hydrochloric acid, or sulfuric acid), and particularly preferredorganic acids include methane sulfonic acid at a concentration of atleast 2.5 to about 4M, and even higher. Preferred separators includethose comprising a perfluorinated polymer that includes sulfonic and/orcarboxylic groups.

In another aspect of the inventive subject matter, contemplated elementsin the cathode compartment particularly include lanthanides, andespecially preferred lanthanides include cerium, praseodymium,neodymium, terbium, and dysprosium. Thus, contemplated batteries willgenerally include an anode, a cathode, a separator, and an acidelectrolyte in which zinc and a lanthanide form a redox pair, whereinthe battery is configured such that during charging of the battery a H⁺flux is generated across the separator that disintegrates a zincdendrite proximal to the separator.

Various objects, features, aspects, and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments of the invention, along with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of an exemplary battery during charge.

DETAILED DESCRIPTION

The inventors have discovered that a battery with a zinc-containing acidelectrolyte can be manufactured such that dendrites growing from theanode during charging will disintegrate proximal to the separator of thebattery.

As used herein, the term “anode” refers to the negative electrode of abattery (i.e., the electrode where oxidation occurs) during discharge ofthe battery. Thus, the term “anode compartment” refers to the batterycompartment that includes the anode, and the term “anolyte” refers tothe electrolyte in the anode compartment. Similarly, the term “cathode”refers to the positive electrode of a battery (i.e., the electrode wherereduction occurs) during discharge of the battery. Thus, the term“cathode compartment” refers to the battery compartment that includesthe cathode, and the term “catholyte” refers to the electrolyte in thecathode compartment.

As also used herein, the term “redox pair” is interchangeably used withthe term “redox couple” and refers to a combination of a first element(or ion of the first element) and second element (or ion of the secondelement) in a battery, in which reduction of the first element andoxidation of the second element produce the current provided by thebattery. The term “first element” as used herein refers to a chemicalelement that may be in ionic form as well as in non-ionic form. Forexample, a preferred first element is zinc, which may be present asmetallic (e.g., plated) zinc as well as ionic zinc (e.g., as Zn²⁺ in asalt with an anion of an organic acid).

Similarly, the term “second element” refers to a chemical element thatmay be in ionic form as well as in non-ionic form. For example, apreferred second element is cerium, which may be present in a firstionic form (e.g., Ce³⁺ in a salt with an anion of an organic acid) aswell as in a second ionic form (e.g., as Ce⁴⁺ in a salt with an anion ofan organic acid). Still further, it is generally contemplated that thefirst and second elements are chemically distinct, i.e., are not thesame chemical element in a different oxidation state. Still further, itshould be appreciated that the term element also includes combination ofone element with a second (or more) elements to form a molecule. Forexample, suitable elements also include metal oxides or metal hydrides.

As still further used herein, the term “H⁺-flux across the separator”refer to a net migration of H⁺-ions through the separator, wherein thedriving force of the migration includes at least one of a concentrationgradient and an electrophoretic force (electrical attraction due toopposite electrical polarity). The term “proximal to the separator” asused herein refers to spatial proximity of an object (e.g., a dendrite)to the separator, wherein the object is generally located between theanode and the separator, and typically within 1 cm from the separator,more typically within 5 mm from the separator and most typically within3 mm or less from the separator. Thus, the term proximal to theseparator also includes contact of the object with the separator.

As still further used herein, the term “disintegrate the zinc dendrite”generally refers to changing the morphology of a zinc dendrite such thatthe changed zinc dendrite looses the ability to puncture or otherwisepenetrate the separator. Most typically, the change of morphology willmacroscopically manifest itself as a crumbling of a zinc dendrite,however, microscopic changes are also contemplated under the scope ofthis definition.

In a particularly preferred aspect of the inventive subject matter, anexemplary battery with autolytic dendrites is depicted in FIG. 1. Here,battery 100 has a cell 101 that is at least partially divided byseparator 130 into an anode compartment 110 and a cathode compartment120. Both anode and cathode compartments include methane sulfonic acid130 in the acid electrolyte 102, wherein the anion of the methanesulfonic acid (MSA⁻) complexes the ionic form of zinc (Zn²⁺) 111A andcerium (Ce³⁺/⁴⁺) 121B and 121A, respectively. The anode compartment 110further comprises anode 160 that is at least partially covered bynon-ionic plated metallic zinc (Zn⁰. The cathode compartment 120comprises cathode 170. Anode 160 and cathode 170 are electricallycoupled to the power source 180, and the arrow above the load indicatesthe flow of the electrons from the anode to the cathode during charge ofthe battery. During charging, dendrites 150 form at the anode 160towards the separator 130 and disintegrate under the H⁺-flux 140 fromthe cathode compartment 120 to the anode compartment 110.

Thus, a particularly preferred battery may comprises a cell with an acidelectrolyte, wherein the cell is at least partially divided by a H⁺permeable separator into an anode compartment and a cathode compartment,wherein the acid electrolyte in the anode compartment comprises zinc,and wherein the acid electrolyte in the cathode compartment comprises anelement that is oxidized during charging of the battery, wherein theoxidized element forms a salt (i.e., forms a complex bond) with an acid,thereby increasing an H⁺ concentration in the cathode compartmentsufficient to promote an H⁺ flux into the anode compartment across theseparator, and wherein the H⁺ flux across the separator is sufficient todisintegrate a zinc dendrite proximal to the separator. Viewed fromanother perspective, preferred batteries will include an anode, acathode, a separator, and an acid electrolyte in which zinc and alanthanide form a redox pair, wherein the battery is configured suchthat during charging of the battery a H⁺ flux is generated across theseparator that disintegrates a zinc dendrite proximal to the separator.

As used herein, the term “the battery is charged” refers to a process inwhich one element is reduced and the other element is oxidized byproviding an electric current such that after charging reduction of oneelement and oxidation of the other element produces a current in thebattery. Viewed from another perspective, the electrochemical redoxreactions in the battery during discharge are reversed during chargingby providing electric current to the battery.

It is generally contemplated that in batteries according to theinventive subject matter zinc will be dissolved into the electrolyteupon discharge of the battery, wherein at least some of the zinc ionswill be complexed by an anion of an acid (e.g., methane sulfonic acid).Consequently, the proton of the acid will be replaced by a complex bond(i.e., a non-covalent, salt-like bond) with the zinc ion. Duringcharging, at least some of the complexed zinc ions will receiveelectrons from the anode, and thus plate onto the anode. Similarly,cerium³⁺ ions will be oxidized during charging to cerium⁴⁺ ions, whereinthe additional positive charge is compensated by a complex bond with ananion of an acid. Thus, oxidation of the cerium will concurrentlyliberate H⁺ from the acid. Equations (I) and (II) below depictschematically the redox reactions during discharging and charging.Discharging: Zn⁰−2e⁻Zn⁺²  (I)Discharging: 2Ce⁺⁴+2e⁻2Ce⁺³  (I)Charging: Zn⁺²+2e⁻Zn⁰  (II)Charging: 2Ce⁺³−2e⁻2Ce⁺⁴  (II)

In an exemplary Zn/Ce redox system using methane sulfonic acid as onecomponent in the electrolyte, it is contemplated that the followingreactions occur during charging (the reactions are reversed ondischarge):Cathode: 2Ce(CH₃SO₃)₃+2CH₃SO₃H2Ce(CH₃SO₃)₄+2H+Anode: Zn(CH₃SO₃)₂ +2H⁺Zn⁰+2CH₃SO₃H

Thus, it should be especially recognized that by employing cerium incontemplated batteries various advantageous properties may be achieved.Among other things, the standard redox potential of the elements incontemplated redox systems (e.g., Ce/Zn) will allow normal operation ofsuch batteries even if the electrolyte from the anode and cathodecompartment are mixed. As used herein, the term “mixed electrolyte”refers to an electrolyte in which the first and second element arepresent in the same compartment (i.e., anode and/or cathode compartment)under normal operating conditions (ie., when the battery is chargedand/or discharged without substantial reduction (i.e., more than 10%) ofelectrode performance and/or battery capacity). The term “normaloperating condition” as used herein specifically excludes operationduring which a separator has been accidentally perforated (e.g., duringcharging).

With respect to the first element in the redox couple (here: Ce) it iscontemplated that suitable elements need not necessarily be limited tocerium, and it is generally contemplated that alternative elements alsoinclude various lanthanides, and especially praseodymium, neodymium,terbium, and dysprosium. Alternatively, suitable lanthanides may alsoinclude samarium, europium, thulium and ytterbium.

Where a lanthanide other than cerium is employed as the redox partnerfor zinc, it is generally contemplated that the concentration of thealternative lanthanide will typically depend, among other factors, onthe solubility of the particular lanthanide and/or the concentration ofa complexing agent (e.g., counter ion, mono- or polydentate ligand,etc.). Thus, it is contemplated that suitable concentrations ofcontemplated non-cerium lanthanides will typically be in the range of 10micromolar (and even less) up to the saturation concentration of theparticular lanthanide (up to 3M, and even higher) in the electrolyte.

Furthermore, it should be recognized that the cost of production ofcontemplated batteries might be significantly reduced by employingmixtures of lanthanides (i.e., by adding at least one additionallanthanide to a lanthanide-zinc redox pair). For example, it iscontemplated that suitable lanthanide mixtures include naturallyoccurring mixtures (e.g., Bastnasite or Monazite), enriched fractions(e.g., Cerium concentrate or Lanthanum concentrate), or mixtures withpredetermined quantities of two or more lanthanides. Mixtures oflanthanides as redox partner with zinc are thought to be especiallyadvantageous where such mixtures include elements with electrochemicallysimilar behavior, or where such mixtures include a predominant fraction(e.g., greater than 80 mol %) of a lanthanide with a desiredelectrochemical behavior. Numerous further aspects of alternative firstelements are described in PCT application entitled “LanthanideBatteries” by Lewis Clarke, Brian J. Dougherty, Stephen Harrison, J.Peter Millington and Samaresh Mohanta, which was filed on or about Feb.12, 2002, and which is incorporated by reference herein.

With respect to the amount of cerium, it is contemplated that the ceriumion concentration may vary considerably and may generally be in therange of between one micromolar (and even less) and the maximumsaturation concentration of the particular cerium ion. However, it ispreferred that the cerium ion concentration in the electrolyte is atleast 0.2M, more preferably at least 0.5M, and most preferably at least0.7M. Viewed from another perspective, it is contemplated that preferredcerium ion concentrations lie within 5–95% of the solubility maximum ofcerium ions in the electrolyte at a pH<7 and 20° C.

It is further contemplated that the cerium ions may be introduced intothe electrolyte in various chemical forms. However, it is preferred thatcerium ions are added to the electrolyte solution in form of a salt,preferably cerium carbonate. However, numerous alternative chemicalforms, including cerium hydrate, cerium acetate, or cerium sulfate arealso contemplated.

With respect to the second element it is generally preferred that zincis the redox partner for cerium (or other first element). However, itshould be appreciated that numerous alternative elements are alsosuitable for use in conjunction with the teachings presented herein, andparticularly preferred alternative elements include titanium andchromium. Other suitable elements include lead, mercury, cadmium, and/ortin. Similarly, the concentration of zinc ions in the electrolyte is atleast 0.05M, preferably at least 0.1M, more preferably at least 0.3M,even more preferably at least 0.5M, and most preferably at least 1.2M.With respect to the particular form of zinc addition to the electrolyte,the same considerations as described above apply. Thus, contemplatedzinc forms include ZnCO₃, ZnAcetate, Zn(NO₃)₂, etc.

In yet another aspect of the inventive subject matter, it iscontemplated that the electrolyte need not be limited to a particularcomposition. However, it is generally preferred that suitableelectrolytes are acid electrolytes (i.e., have a pH of less than 7.0),and it is contemplated that numerous organic and inorganic acids may beused.

It should be particularly recognized that suitable acids in the acidelectrolyte may vary considerably. However, it is generally preferredthat contemplated acids will be able to dissolve (i.e. to form complexbonds with) at least one ionic species in the redox couple, Especiallycontemplated acids will (a) form a complex bond with the oxidizedelement in the cathode compartment, and (b) deprotonate upon formationof the complex bond with the oxidized element. Viewed from anotherperspective, it should be appreciated that preferred acids exchange aproton for a complex bond with the oxidized element in the cathodecompartment. Still further, it is preferred that the anion of the acidnot only forms a complex bond with the oxidized element in the cathodecompartment, but also forms a complex bond with the reduced element inthe cathode compartment.

Similarly, it is contemplated that the same type of acid may also beemployed in the anode compartment, wherein the anion of the acid willform a complex bond with at least one of the oxidized and reduced formof the element in the anode compartment. However, it should beappreciated that the element in the anode compartment may also bereduced to an electroneutral element (e.g., plated as a metal).Furthermore, while it is generally preferred that the anode and cathodecompartment include the same type of acid, it should also be recognizedthat the acids in the anode and cathode compartments may be chemicallydistinct. Thus, suitable acids include organic and inorganic acids, andany reasonable combination thereof.

Consequently, it should be recognized that suitable acids incontemplated acid electrolytes not only provide a particular pH for aparticular redox couple, but also exhibit at least one of two additionalfunctions. The first additional function of contemplated acids is toincrease the solubility of at least one of the first and second elementsof the redox couple by forming a complex bond with the at least one ofthe first and second elements in the oxidized and/or reduced state. Thesecond additional function of contemplated acids is to provide a sourceof protons that is liberated from the acid in response to oxidation ofthe redox element in the cathode compartment. Thus, it should berecognized that the protons from an acid in the acid electrolyte in thecathode compartment will increase acidity in the anode compartment, andespecially proximal to the separator such that dendrites forming fromthe anode during charging will disintegrate.

An especially preferred organic acid that dissolves ceric and cerousions (as well as other high energy redox ions, e.g., Ti³⁺, or Cr²⁺) at arelatively high concentration is methane sulfonic acid at a relativelyhigh concentration (i.e., at least 50 mM, more preferably at least 100mM, and most preferably at least 1M). With respect to the concentrationof the MSA or other acid it should be appreciated that a particularconcentration of MSA is not limiting to the inventive subject matter.However, a particularly preferred concentration of methane sulfonic acidis in the range of between 1M and 4M, and more preferably between 2.5Mand 3.5M. In further alternative aspects of the inventive subjectmatter, it is contemplated that EDTA or alternative chelating agentscould replace at least a portion, if not all of the methane sulfonicacid in at least the zinc cathode part of the cell.

Alternative organic acids include trifluoromethane sulfonic acid(CF₃SO₃H), which may make a better solvent anion than methane sulfonicacid for ceric ions and would make an excellent high energy battery forspecial applications. Still further contemplated acids include inorganicacids such as perchloric acid (HClO₄), nitric acid, hydrochloric acid(HCl), or sulfuric acid (H₂SO₄). However, such alternative acids mayimpose safety concerns or exhibit less advantageous capability todissolve high concentrations of ceric ions.

In still further alternative aspects, it is contemplated that theelectrolyte may also be gelled, and that preferred gelled electrolytesinclude one or more anions of an organic or inorganic acid. Varioussuitable methods and compositions for gelled electrolytes are disclosedin the PCT patent application entitled “Improved Battery With GelledElectrolyte” by Lewis Clarke, Brian J. Dougherty, Stephen Harrison, J.Peter Millington and Samaresh Mohanta, which was filed on or about Feb.12, 2002, which is incorporated herein by reference.

While in some battery configurations a NAFION™ (copolymer ofperfluorosulfonic acid and polytetrafluoroethylene) membrane may operatemore satisfactorily than other membranes, it is generally contemplatedthat the exact physical and/or chemical nature of the membrane is notlimiting to the inventive subject matter so long as such membranes allowH⁺ exchange between an anode and cathode compartment in contemplatedacidic electrolytes. Consequently, it should be appreciated thatnumerous alternative membranes other than NAFION™ are also suitable, andexemplary membranes include all known solid polymer electrolytemembranes, or similar materials.

Moreover, it should be especially recognized that in contemplatedbatteries membranes are suitable for use even if such membranes exhibitsome leakage or permeability for catholyte and/or anolyte into theopposite compartment, since contemplated batteries are operable evenunder conditions in which the electrolytes are mixed (supra). Variousaspects of mixed electrolytes in contemplated batteries are disclosed inthe PCT patent application entitled “Mixed Electrolyte Battery” by LewisClarke, Brian J. Dougherty, Stephen Harrison, J. Peter Millington andSamaresh Mohanta, which was filed on or about Feb. 12, 2002, which isincorporated herein by reference.

With respect to the cell it is contemplated that the particular formsand material will be at least partially determined by the particularfunction of the battery. However, it is generally contemplated that thecell is fabricated from a material having sufficient chemical stabilityto withstand the electrochemical processes and acidity of contemplatedbatteries without structural damage that would result in significantloss of battery function (e.g., loss of electrolyte, leaking of materialcomponents into the electrolyte and subsequent plating or precipitationof such materials, etc.). Thus, particularly preferred materials includeacid resistant high-density polymers, which may or may not be coated.

In yet further alternative aspects of the inventive subject matter, itis contemplated that suitable batteries may be configured in a batterystack in which a series of battery cells are electrically coupled toeach other via a bipolar electrode. The particular nature of the bipolarelectrode is not limiting to the inventive subject matter, and it isgenerally contemplated that any material that allows for oxidation ofcerous ions to ceric ions during charging (and the reverse reactionduring discharge) and plating/de-plating of zinc is suitable for useherein. However, a particularly preferred material for a bipolarelectrode is glassy carbon (carbon that exhibits has no long-range orderin three dimensions). The inventors surprisingly discovered that glassycarbon provides, despite operation in a highly acidic electrolyte, anexcellent substrate for plating of zinc during charging. Furthermore,glassy carbon is a relatively inexpensive and comparably light-weightmaterial, thereby further improving the ratio of cost/weight tocapacity. Various contemplated aspects of bipolar electrodes aredisclosed in US provisional patent application with the title “ElectricDevices With Improved Bipolar Electrode” by Lewis Clarke, Brian J.Dougherty, Stephen Harrison, J. Peter Millington and Samaresh Mohanta,which was filed on or about Feb. 12, 2002, which is incorporated byreference herein.

Particularly useful applications of the inventive subject matterpresented herein include the use of contemplated electrolytes andelectrodes in various battery types. For example, where the capacity ofcontemplated batteries is relatively high, it is contemplated that suchelectrolytes and electrodes may be employed in various load-leveling andstand-by battery configurations. On the other hand, contemplatedelectrolytes and electrodes may also be employed in primary andsecondary battery types that are useful for household, automotive, andother uses where a relatively small battery capacity is required.Various aspects of configurations and use of contemplated batteries withespecially high capacity is described in pending PCT application withthe title “improved load leveling battery and methods therefor”, serialnumber PCT/US01/41678, which is incorporated by reference herein.

Experiments

To validate the concept of a secondary battery with autolytic dendrites,a cell was constructed by using four blocks of plastic Ultra HighMolecular Weight Polyethylene (UHMWP), with gaskets in between eachface, two electrodes, and one Nafion® membrane. Electrolyte inlets andoutlets were made in the center sections and electrolyte was fed fromtwo small tanks via a peristaltic pump into the respective compartments.

The cerium solution contained 106 grams Ce₂(CO₃)₃ *5H₂O in 480 mlmethane sulfonic acid and 320 ml of water. The zinc solution contained65 grams zinc carbonate in 240 ml methane sulfonic acid and 160 ml ofwater. The ceric solution was fed to the cathode made of coated titaniummesh (TiO₂), and the zinc solution was fed to the anode. Cell gap was2.54 cm, flow rate about 2 liter per minute.

The cell was charged at 0.5A (current density is 50 mA/cm²) for fivehours. The colorless cerous methane sulfonate turned yellow and the opencircuit cell voltage was 3.33 volts. Only 3 grams of zinc would havebeen deposited by this time if the cell were running at 100% currentefficiency. The cell was further run overnight at 0.2A current and anadditional 5 hours at 0.5 A. The open circuit voltage maximum was 2.46 Vand the voltage across the cell during charging at 0.5 A was 2.7 V. Toinvestigate the current efficiency, the cell was emptied and the anodeside was inspected. The anode side contained approximately 9 grams ofzinc, which is in very close agreement with the theoretical valueexpected for the charge passed. The zinc was placed in the electrolyteand the rate of spontaneous dissolving of the zinc was relatively slow.About 50% of the zinc was still observed after two hours, and someresidual zinc remained after 72 hours.

After numerous charge/discharge cycles, growth of zinc dendrites at theanode was observed while the battery was charged. Surprisingly, however,substantially all of the dendrites disintegrated prior to contact withthe separator. While not whishing to be bound by any particular theoryof hypothesis, the inventors contemplate that the dendrites aredisintegrated under the influence of e relatively high H⁺ concentrationproximal to the separator. Consequently, it should be appreciated thatthe zinc dendrites in contemplated secondary batteries disintegrate atan increasing rate when charging of the battery is increased.

Still further, very little gassing at the anode or cathode was observedduring the charging process. Most of the zinc formed granular nodules onthe titanium anode and eventually plated on the face of the membrane,while the ceric cathode appeared to be substantially free of deposits.

Thus, specific embodiments and applications of mixed electrolytebatteries have been disclosed. It should be apparent, however, to thoseskilled in the art that many more modifications besides those alreadydescribed are possible without departing from the inventive conceptsherein. The inventive subject matter, therefore, is not to be restrictedexcept in the spirit of the appended claims. Moreover, in interpretingboth the specification and the claims, all terms should be interpretedin the broadest possible manner consistent with the context. Inparticular, the terms “comprises” and “comprising” should be interpretedas referring to elements, components, or steps in a non-exclusivemanner, indicating that the referenced elements, components, or stepsmay be present, or utilized, or combined with other elements,components, or steps that are not expressly referenced.

1. A battery comprising: a cell with an acid electrolyte, wherein thecell is at least partially divided by a H⁺ permeable separator into ananode compartment and a cathode compartment; wherein the acidelectrolyte in the anode compartment comprises zinc, and wherein theacid electrolyte in the cathode compartment comprises an element that isoxidized during charging of the battery, and wherein oxidation of thezinc and reduction of the oxidized element produce current provided bythe battery; wherein the acid electrolyte comprises an acid that has achemical composition effective to form a salt with the oxidized elementin an amount effective to increase an H⁺ concentration in the cathodecompartment sufficient to promote an H⁺ flux into the anode compartmentacross the separator; and wherein the separator is configured such thatthe H⁺ flux across the separator is sufficient to disintegrate a zincdendrite proximal to the separator.
 2. The battery of claim 1 whereinthe acid electrolyte comprises an organic acid.
 3. The battery of claim1 wherein the acid electrolyte comprises an acid selected from the groupconsisting of methane sulfonic acid, trifluoromethane sulfonic acid,perchloric acid, nitric acid, hydrochloric acid, and sulfuric acid. 4.The battery of claim 1 wherein the H⁺ permeable separator comprises aperfluorinated polymer.
 5. The battery of claim 1 wherein the element inthe cathode compartment is a lanthanide.
 6. The battery of claim 5wherein the lanthanide is selected from the group consisting of cerium,samarium, and europium.
 7. The battery of claim 2 wherein the organicacid is methane sulfonic acid and the element in the cathode compartmentis cerium.
 8. The battery of claim 2 wherein the organic acid is presentin the cathode compartment at a concentration of between 1M and 4M. 9.The battery of claim 2 wherein the organic acid is present in thecathode compartment at a concentration of between 2.5M and 3.5M.
 10. Thebattery of claim 2 wherein the organic acid is present in the anodecompartment at a concentration of at least 2.5M and forms a salt withoxidized zinc upon discharge of the battery.
 11. A battery comprising ananode, a cathode, a separator, and an acid electrolyte in which zinc anda lanthanide form a redox pair, wherein the battery is configured suchthat during charging of the battery a H⁺ flux is generated across theseparator that disintegrates a zinc dendrite proximal to the separator,and wherein oxidation of the zinc and reduction of the lanthanideproduce current provided by the battery.
 12. The battery of claim 11wherein the lanthanide is selected from the group consisting of cerium,samarium, and europium.
 13. The battery of claim 11 wherein theelectrolyte comprises methane sulfonic acid, wherein charging of thebattery oxidizes Ce³⁺ to Ce⁴⁺, and wherein the methane sulfonic acidcomplexes Ce⁴⁺ thereby releasing H⁺ that passes through the separator.14. The battery of claim 11 wherein the acid electrolyte is a mixedelectrolyte, and wherein the mixed electrolyte contacts at least one ofthe anode and cathode.